In a mail sorting system, the mail pieces to be sorted are essentially flat rectangular objects arranged together with their planar surfaces along a common axis to form a stack. A feeder mechanism picks off individual mail pieces from an input stack to an optical reader which reads the address printed on the mail piece and directs the mail piece to one of several output stacks corresponding to the destination address. In the mail handling apparatus, the mail items should be transferred individually. However, due to the high feed rate or diverse product shape (length, width, height, and thickness) and composition (material, form), the rate of overlapped (double feed) mail transfer can also be high. When a plurality of mail items are transferred in an overlapped manner to the handling apparatus, the handling apparatus cannot perform its normal operation.
Currently available double feed detection systems are either expensive and require complex setups (for example, digital cameras that analyze digital images of the passing items), or are unreliable because they are limited to detecting items that have specific shapes, colors, thicknesses, are of a particular type and are not fully overlapped with each other, or cannot accurately detect more than two overlapped items. These limitations increase the number of undetected overlapped items as well as the number of incorrectly (unwarranted) rejected items. Therefore, it would be advantageous to have a detection system, apparatus, and method that accurately detects mail characteristics, including edges, as early as possible in the feed path, in order to determine conditions, such as double feed (overlap of one or more mail pieces).